This invention relates to a thermal (heat-sensitive) transfer recording medium, more specifically it relates to a thermal transfer recording medium having a backing layer.
Heretofore, at a back surface of the thermal transfer recording medium used in the thermal transfer recording system, in order to prevent a phenomenon of which a back surface of a support and a thermal head are fused at transfer (so-called sticking phenomenon) or a phenomenon of which a back surface of a support and a thermal transfer colorant layer contacted thereto, stick together when wound-up for storage (so-called blocking phenomenon), and to make smooth running property in a cassette, a backing layer has been provided at the back surface of the support.
Generally speaking, the backing layer has been formed by coating a resin component containing a powdery substance on a surface where no thermal transfer colorant layer has been provided.
As the resin component for forming such a backing layer, various resins such as an acrylic series resin, a polyester series resin and a cellulose derivative have generally been used.
On the other hand, as the powdery material, inorganic powder such as silica powder, boron nitride powder, talc and aluminum dioxide powder has generally been used.
However, according to the investigation of the present inventors', it was found that since the above inorganic powder has high hardness, a device which contacts to the backing layer, such as a thermal head is damaged, and particularly usable lifetime of the thermal head has shortened. Further, when the backing layer and the thermal transfer colorant layer has contacted for a long time, surface state of the backing layer has sometimes transferred to the thermal transfer colorant layer. In such a case, it was found that surface smoothness of the thermal transfer colorant layer has been damaged so that adhesive property between a medium to be transferred and a thermal transfer recording medium has been lowered, and thus printing quality has also been lowered.
Further, the inorganic powder is generally low in dispersibility to a resin component. If one wishes to disperse the inorganic powder in those which are widely used as a resin for the backing layer, it sometimes does not disperse therein. Such an inorganic powder which is badly dispersed falls away during running so that inner portion of the device is sometimes stained. Moreover, the inorganic powder which is badly dispersed may sometimes cause lowering printing quality by adhering to a surface of the thermal transfer colorant layer after long term contact between the backing layer and the thermal transfer colorant layer.
Also, these inorganic powders are low in dispersibility in a resin component such as a silicone series resin having good heat resistance, and it is difficult to disperse well therein by the conventional method. Accordingly, it is the present situation that in the backing layer used a resin having a good heat resistance such as a silicone series resin, it has not been investigated concretely to use and add a powdery particle.
On the other hand, in the thermal recording method used a thermal transfer recording medium, there has heretofore been involved a problem that printing quality to a transfer paper which is low in surface smoothness (so-called rough paper) is insufficient. In order to solve this problem, the method of improving printing quality to the rough paper involved an extreme increase in the printing energy used.
A thermal energy in this case is extremely high as compared with the required printing energy used with a transfer paper which is high in surface smoothness. Therefore, if a thermal transfer recording medium having a backing layer formed by the conventionally employed resin component, new problems have been caused that thermal deformation in the thermal transfer recording medium such as causing wrinkle at the printed portion due to a thermal energy at transfer is generated.
When deformed thermal transfer recording medium is wound (after use), wound diameter after use becomes larger than that before use (fatten by wind up). Accordingly, in the case that the thermal transfer recording medium used at high energy transfer is contained in a cassette and used, the thermal transfer recording medium which is a thermal tape shall be contained in the cassette by previously deducting an increase of wound diameter due to fatten by wind up after use of the thermal transfer recording medium.
In the thermal transfer recording medium used in the form of a cassette, it is advantageous that printing quantity is large per one cassette. However, by considering fatten by wind up, to remain surplus space in a cassette while maintaining a size of the conventional cassette is disadvantageous with respect to the printing quantity. But the surplus space considering fatten by wing up is provided to the conventional cassette, increase in the cassette size, and yet increase in the printer size will be caused.